Forced air hydronic furnace efficiency

[Rick]

We have just moved into a new townhouse -- a condo, but we own the hot water heater and furnace. The furnace is a strange beast that uses as its heat source water from the hot water heater! (The water heater is gas.) I think this is called hydronic forced air, but there is very little on the internet about it. I talked to our furnace guy at the house we had previously and he said they were cheap to install but very inefficient! I think he was right -- we are using more gas to heat this place than we did in the house. It is smaller and has two shared walls, so should not use nearly as much gas! Does anyone know anything about these furnaces? btw, this is a brand new (well, three years old) townhouse -- not an old one. I think we will have to replace the furnace soon. :-(

[bud21ca]

Those systems are usually run from a boiler that heats the water, then the hot water is piped to an air handler (looks just like a furnace) which then takes the heat and blows it around. These systems are usually very efficient.

[wgauci]

I've only seen a few of these units in houses but they seem to becoming more popular. Unfortunatley they're only as efficient as the water heater that's supplying the fan coil. TKG might have more experience and a better handle on exactly how efficient they really are, but to me the best set up with this type of system is to have a dedicated boiler feeding in-floor heat with the fan coil in the furnace as a secondary heat source. The one customer I remember seeing with your type of system went through his first water heater in 5 years. I don't feel that there are many tank type water heaters that can handle the constant duty that a forced air furnace system puts on them and it really shortens the life as a result.

If you're looking to upgrade, I'd look into a dedicated boiler system to supply the hot water to the fan coil and they can install a small plate type heat exchanger that's very efficient that will heat your potable water. You could do it with instant or a storage tank. You might even want to look into how feasable it is to add some in-floor heat loops in your basement if you're using it for living. It sounds like you got the econo set up by the builder.

[txv]

What kind of water heater is it connected to?

If it's a standard efficiency direct vent, power vent, or natural draft water heater, the system is inefficient.

Look for an energuide label or energy factor rating on the water heater. (Typical EF is 0.55 - 0.62, energy efficient is 0.9 or greater)

With a 90%+ efficient boiler or water heater (many of them look like tankless water heaters), a hydro air system is as good as a modern furnace.

Keep the system for a while to see what the gas bills are like.

[Rick]

It is not a boiler, but a standard water heater - a Rheem PowerVent PVR50-80. I cannot see any information about efficiency, nor can I find that information on the web.

During the recent quite cold weather, it is running nearly constantly (the temperature is set to 20 deg day, 18 deg night) Since Jan 9 we have used 277 cubic metres of gas which is about 16 cubic metres per day. I never measured it daily at our previous house, but the highest monthly amount last winter averaged about 15 cubic metres per day. (That was a standard suburban 3 bedroom house but with a very high efficiency Carrier furnace.) So this definitely seems high. I have been thinking that we should get an energy audit to see if there are particular things we could improve. Can't do much in a condo since all exterior stuff is not ours.

[TKG26]

That tanke is rated for combo heating, with a 80,000BTU burner this is a high input pv50 They are about 60-65% eff. Not sure why they did not go with a high effecieny combo heater such as the Polaris tanks.

Im not a big fan of heating hot water to then heat air with an air handler... But if sized properly that can work quite well.

Might be worth having a tech into look at the system. I find improperly installed equipment all the time....

[txv]

That take is rated for combo heating, with a 80,000BTU burner this is a high input pv50 They are about 60-65% eff. Not sure why the did not go with a high effecieny combo heater such as the Polaris tanks.

High efficiency furnaces are required by code in new construction but builders are allowed to do that?!

Must be a loop hole.

[Rick]

This townhouse is part of the Radio City complex, built by Context Developments. We understand that their construction leaves a lot to be desired!! :-(

Do the Polaris water heaters require an input for combustion? The current water heater only has a vent -- it uses interior air for the combustion. Adding another pipe for input would be tricky, to say the least!! That is one of the things I have been worried about in thinking about replacing the furnace. I looked at some info about the Polaris heaters which claims they are 95% efficient. Sounds good!

[whollycheeses]

The Polaris water heaters pull their combustion air from the outside. I believe the current code in Ontario is anything over 50,000 btu must pull combustion air from outside and the Polaris heaters are well over 100,000+ btu.

I lived with one of these systems (Polaris with air handler) for 10 years (also builder installed in my townhouse) and it never ran longer than 2 years without a break down. It was always the HSI (hot surface igniter) that would go, and of course it would always be in Jan or Feb so we not only had no hot water, but no heat as well.

At 10 years it had a crack in the heat exchanger so Enbridge 'red tagged' it, and I replaced it with a Carrier furnace and regular power vent water heater. That was 5 years ago and we've had no problems since. I'm so glad to be rid of that thing.

In many ways it's similar to a tankless water heater in that it works great in theory, but not in practice. Don't hesitate to replace.

[TKG26]

I agree the polaris has service issues. Its actually strange we have areas where we are never in for service calls on these tanks and in some areas we are they all the time. The big pain is once they shut down you loose hot water and heat.

HSI failures is probably the most common problem with them and the cracking of heat exchangers.... When they work they are pretty nice. A alternative would be the Lennox Complete Heat

As for combustion air that 80,000btu tank would require combustion air, look around you probably have a 4-5" round pipe in that furnace room. The polaris uses either a 2 pipe system or a concentric(2in1 vent)system

If your looking for a replacement i would opt for a stand alone furnace and water heater.(or a tankless heater)

[txv]

A alternative would be the Lennox Complete Heat

According to what I have read on HVAC forums and elsewhere, the complete heat was a service/reliability nightmare. Apparently lennox discontinued it.

What about using a high efficiency tankless heater with two separate loops? (DHW never touches water used for heating)

[TKG26]

We had limited number of complete heats in our rental program, they had some issues but nothing terribly hard to fix, much easier to work on standing up rather then standing on your head to fix a polaris! LOL I think your right though lennox dropped them, we still have many in service though, ignitors and pumps are there main issues

[DJDiggler]

Just a reminder to the OP, if you do replace your current system with a HE furnace and Hot water tank, you can claim bolth the energy efficiency rebate AND the new home improvement/renovation one (should apply?)! Could be a much more affordable upgrade now.